perf: use class_traits with a cache to speed up creation of widgets

ipywidgets/widgets/tests/test_traits.py

@@ -11,7 +11,7 @@
 from traitlets import HasTraits, Int, TraitError
 from traitlets.tests.test_traitlets import TraitTestBase
 
-from ipywidgets import Color, NumberFormat
+from ipywidgets import Button, Color, NumberFormat
 from ipywidgets.widgets.widget import _remove_buffers, _put_buffers
 from ipywidgets.widgets.trait_types import date_serialization, TypedTuple
 
@@ -243,3 +243,13 @@ class TestCase(HasTraits):
 
     obj = TestCase()
     assert obj.value == (1, 2, 3)
+
+
+def test_add_trait():
+    button = Button()
+    keys = list(button.keys)
+    assert 'foobar' not in keys
+    button.add_traits(foobar=Int().tag(sync=True))
+    assert 'foobar' in button.keys
+    assert 'foobar' not in Button().keys
+    assert set(button.keys) != set(keys)

ipywidgets/widgets/widget.py

@@ -10,6 +10,7 @@
 from collections.abc import Iterable
 from IPython import get_ipython
 from ipykernel.comm import Comm
+import functools
 from traitlets import (
     HasTraits, Unicode, Dict, Instance, List, Int, Set, Bytes, observe, default, Container,
     Undefined)
@@ -367,7 +368,7 @@ def get_view_spec(self):
 
     @default('keys')
     def _default_keys(self):
-        return [name for name in self.traits(sync=True)]
+        return [name for name in self.class_traits(sync=True)]
 
     _property_lock = Dict()
     _holding_sync = False
@@ -483,7 +484,7 @@ def get_state(self, key=None, drop_defaults=False):
         else:
             raise ValueError("key must be a string, an iterable of keys, or None")
         state = {}
-        traits = self.traits()
+        traits = self.class_traits()
         for k in keys:
             to_json = self.trait_metadata(k, 'to_json', self._trait_to_json)
             value = to_json(getattr(self, k), self)
@@ -547,6 +548,13 @@ def add_traits(self, **traits):
                 self.keys.append(name)
                 self.send_state(name)
 
+    @classmethod
+    @functools.lru_cache(None)
+    def class_traits(cls, **metadata):
+        # we cache it for performance reasons
+        return super().class_traits(**metadata)
+
+
     def notify_change(self, change):
         """Called when a property has changed."""
         # Send the state to the frontend before the user-registered callbacks
@@ -682,7 +690,7 @@ def _send(self, msg, buffers=None):
             self.comm.send(data=msg, buffers=buffers)
 
     def _repr_keys(self):
-        traits = self.traits()
+        traits = self.class_traits()
         for key in sorted(self.keys):
             # Exclude traits that start with an underscore
             if key[0] == '_':